Designers of camera modules are perpetually faced with the challenge of packaging components inside a small envelope. Recently, the camera manufacturing industry has seen a rapid decrease in the size of component envelopes. One reason for the rapid pace of ever-shrinking camera technology has been the integration of camera technology and miniature consumer electronic products, such as cellular telephones with a digital camera incorporated therein. Furthermore, there is an ever-increasing trend to install miniature cameras in a wide variety of other consumer products not ordinarily associated with typical camera applications.
Some of the parts used in a miniature camera include: a lens package containing the lenses needed for the given application, an imaging device and a barrel housing to house the lens package and to allow optical communication between the lens package to the imaging device. Further, it is desirable for the manufacturers of the miniature cameras to be able to mass produce camera modules. Often times, however, mass production results in small differences in size of the module components and size differences from the manufacturing process. Therefore, post assembly focusing is needed to adjust the focal point (back focal length) of mass-produced lens packages to account for tiny differences in the manufactured part and based on the differences needed in given specific applications. Also, it is desirable for the camera module manufacturers to be able to achieve these goals while maintaining high-quality standards, reliability and commercial feasibility.
Various solutions have been proposed to solve the problems associated with manufacturing ultra-compact camera modules with the ability to focus assembly parts after they are assembled. One approach used to decrease the size of the module utilizes traditional wire bonding technology and integrates the imaging device onto a substrate which contains other necessary electronic components. Examples of this substrate may include ceramic, BT, FR4, etc. Those having ordinary skill in the art will recognize that any suitable substrate may be used. However, this approach wastes space. For example, an imaging device comprised of an array of charge-coupled devices (CCD) or an array of CMOS sensors include some amount of space around the array for contact attachment pads used in the wire bonding method. Such placement forces the designer of the integrated chip and camera module to position the components around the extra space, thus taking up more space.
Other approaches used to provide an ultra-compact camera module having the ability to focus the manufactured parts utilizes a lens package with a barrel housing and a rotatable lens barrel. One approach utilizes a barrel housing having an internal thread surface and lens barrel having an external thread. According to this approach, the lens barrel is screwed into the barrel housing until the focal point of the lens package falls on the appropriate point. In another approach, the barrel housing has a ramp design and the lens barrel is rotated within the barrel housing which causes the lens barrel to move up the ramp. This movement adjusts the lens barrel in order to obtain the appropriate focal point.
However, these solutions cannot be applied to applications having angularly position-sensitive components. For instance, applications utilizing an array of charge-coupled devices (CCD) or CMOS sensors as the imaging device often times require that the imaging device and the actuator assembly be precisely aligned prior to adjusting focal point to account for the differences noted above. In this case, the precise alignment will be compromised by rotating the lens barrel to adjust the focal point.
Some camera module manufacturers have utilized resilient structures to adjust the focal point of a lens package. According to one method, a lens barrel is placed within a barrel housing which includes a resilient structure such as cushion or springs. The lens barrel is moved up or down to adjust the focal point of the system. As such the resilient structures either compress or expand based on the position of the lens barrel. This method presents a number of problems. First, once the focal point of the system is found, the pressure applied to the resilient structure must be maintained at a constant while the lens barrel is locked in place. Next, the pressure applied to the structures is often achieved by screwing the lens barrel into the housing barrel. Again, this causes unwanted rotation of the lenses in relation to the imaging device. Other methods of using resilient structure lack reliability due to creep damage and fatigue effects that occur to the resilient material, which, over time decreases the reliability of the camera.
What is needed is a method to effectively adjust the focal point of camera modules while maintaining an ultra-compact envelope, precise alignment of the lens package in relation to the imaging device and reliability of the integrity of the adjusted parts.